Transducer-based sensor system

ABSTRACT

A transducer-based sensor system including a drive signal generator for generating a drive signal, a transducer coupled to the drive signal generator and configured to receive the drive signal, a mixer coupled to the transducer and configured to receive output from the transducer where such output results at least in part from physical movement of the transducer, and a diplexer operatively coupled with an output of the mixer and configured to present a substantially matched output impedance to the mixer over an operative range of output frequencies.

BACKGROUND

[0001] Transducer devices are used in a variety of applications totransfer energy between electrical systems and mechanical systems.Quartz crystal microbalance (QCM), for example, is a transducer-basedtechnology that may employ piezoelectric transducers in variousconfigurations to perform sensing functions. QCM technology takesadvantage of the fact that the resonant frequency of a transducertypically varies with the effective mass of the transducer. Accordingly,when portions of a sample material bind to the transducer, the mass ofthe bonded sample material can be detected by monitoring the resonantfrequency of the vibrating mass, relative to a predetermined reference.

[0002] A related technology is rupture event scanning (RES), in whichtransducers may be employed to produce mechanical energy to break bondswithin a sample material. In addition to providing energy to break thebonds, the transducers may be used as sensors to analyze acoustic events(e.g., a pressure wave) that can occur when bonds break. Different typesof bonds have unique properties that produce distinctive acousticevents. The bonds can be identified and analyzed by using varioustechniques to study the acoustic events.

[0003] Transducer systems such as those described above typically employmultiple distinct transducers. The transducers are often provided in anarray, with some type of mechanical suspension being used to suspend thetransducers in place relative to a base or other stationary component ofthe system.

[0004] Although many prior systems have multiple transducers, typicallyonly one transducer can be activated at any given time. Alternatively,where multiple transducers are simultaneously active, the activatedtransducers commonly must be separated by a relatively large physicaldistance. The reason for this is to avoid undesired signal coupling thatcan occur when physically proximate transducers are active at the sametime.

[0005] One type of undesired coupling results from the liquid that isoften used to hydrate biological samples in QCM and RES applications.Where a well of liquid is spread across multiple transducers, or evenwhere separate liquid wells are employed for each transducer in amultiple-transducer configuration, mechanical vibration produced by onetransducer can be transmitted through the liquid (and throughintervening structures) to other transducers in the system. Accordingly,when the transducers are simultaneously activated, the electrical signalproduced at the second transducer will include interference produced bythe vibration of the first transducer. The mechanical suspension thatholds the transducers in place can also transmit vibration from onetransducer to another, even though such suspensions typically aredesigned to minimize this effect. Finally, stray capacitance, straymutual inductance and other indirect electrical coupling can produceinterference when physically proximate transducers are activatedsimultaneously.

[0006] Because prior systems typically do not provide for simultaneousactivation of physically proximate transducers, they may be limited inprocessing speed and may not be able to provide a satisfactory level ofperformance in applications where it is desirable to operate multipletransducers at the same time.

[0007] In some prior systems, resolution is limited by the drive signalused to activate the transducers. In particular, the fabrication processand other factors may lead to variations in the resonant frequencies ofthe transducers in the system. Failure to accommodate these variationscan diminish the resolution and/or accuracy of the sensor system.Specifically, when a transducer is activated at frequencies other thanits resonant frequencies, the resulting vibration will be less than themaximum possible amount. This can result in lower resolution outputsignals that are more susceptible to noise.

[0008] Other transducer-based sensor systems and methods suffer fromdisadvantages relating to impedance within the output signal paths forthe transducers. In many cases, the impedances within the output signalpaths are matched for only a narrow range of output signals. As aresult, mismatches and incomplete terminations occur when output signalshave characteristics falling outside this range (e.g., frequencies thatare higher or lower than the expected range of output frequencies). Thesignal reflections and other artifacts that can result from theimpedance mismatches can significantly complicate the processing ofoutput signals, and can hinder rejection of unwanted noise components.

SUMMARY

[0009] A transducer-based sensor system is provided which includes adrive signal generator for generating a drive signal, a transducercoupled to the drive signal generator and configured to receive thedrive signal, a mixer coupled to the transducer and configured toreceive output from the transducer where such output results at least inpart from physical movement of the transducer, and a diplexeroperatively coupled with an output of the mixer and configured topresent a substantially matched output impedance to the mixer over anoperative range of output frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic depiction of an embodiment of atransducer-based sensor system.

[0011]FIG. 2 is a schematic depiction of an embodiment of a transducerarray, including a plurality of transducer groups, which may beconfigured similarly to the transducer group shown in FIG. 1.

[0012]FIG. 3 depicts an exemplary implementation of amultiple-transducer sensing method, in which multiple transducers may beemployed at the same time.

[0013]FIG. 4 is a schematic depiction of another embodiment of atransducer-based sensor system.

[0014]FIG. 5 depicts an exemplary implementation of anothertransducer-based sensing method.

[0015]FIG. 6 schematically depicts an exemplary circuit that may beemployed to perform sequentially alternating transmission and receptionof transducer signals.

[0016]FIG. 7 schematically depicts an exemplary circuit that may be usedto sample output from a transducer while simultaneously applying aninput drive signal to the transducer.

DETAILED DESCRIPTION

[0017]FIG. 1 depicts an exemplary sensor system 10, including a group 12of transducers 12 a, 12 b, 12 c and 12 d. The transducers may be placedinto contact with, or in close proximity to, a test material such assample 14. The test material may be provided as one contiguous samplespread across multiple transducers, or may be provided as separateportions 14 a, 14 b, 14 c and 14 d in a well, receptacle or likecontainer associated with each transducer, as in the depicted example.Typically, the transducers are coupled with a signal generator, such asoscillator subsystem 16, via which activating signals are applied to thetransducers. The transducers typically are also coupled with additionalelectronic components adapted to facilitate sensing functions, as willbe explained in detail below.

[0018] The depicted transducers may take a variety of configurations,and may be implemented in different sizes and shapes, and with differentmaterials, as desired and appropriate for a given application. In someembodiments, the transducers are implemented within a microchip as anarray of piezoelectric crystals, or as an array of surface acoustic wavedevices, surface-skimming bulk wave devices, Love-wave devices or othertransducer devices. FIG. 2 depicts such an exemplary array 20, includinga plurality of groups 22 of transducers. As with the exemplary groupshown in FIG. 1 (i.e., group 12), each of the groups shown in FIG. 2 mayinclude four transducers. Alternatively, any other practicable number oftransducers may be employed within the individual groupings. Insingle-chip embodiments, the supporting electronics typically areimplemented at least partially on the chip along with the transducers.

[0019] Referring again to FIG. 1, the activating signals applied fromoscillator subsystem 16 may cause the transducers to vibrate or undergoother movements. Typically, movement of the transducers is dependent notonly on the characteristics of the activating signal, but also on thephysical characteristics of the transducer and/or on physical phenomenaoccurring around the transducer. For example, the response of atransducer to a given activation signal will depend on the resonantfrequency of the transducer. Resonant frequency, in turn, varies withthe mass bound to the transducer. Accordingly, the character of atransducer's vibration may be affected by matter that bonds to thesurface of the transducer to thereby vary the effective mass of thetransducer. In addition, phenomena occurring within sample 14, or at thesurface of the transducer, can affect transducer movement. For example,breaking of chemical bonds can produce a sonic event (also referred toas an acoustic event) that can contribute to the vibratory movement of atransducer.

[0020] In typical embodiments, vibrations and other movement may produceelectrical output signals on output lines 18 a, 18 b, 18 c and 18 d.Analysis of these electrical signals can produce valuable informationabout sample 14. For example, such analysis can yield information aboutwhether, and to what extent, portions of the sample have bonded to thesurface of the transducers. Information may also be obtained aboutwhether the sample contains certain types of matter, for example, byanalyzing signals produced by rupture and other events.

[0021] In many applications, to achieve sufficiently accurate sensing,it will be desirable that the signal on any given transducer output line(e.g., lines 18 a, 18 b, 18 c or 18 d) correspond only to physical andelectrical occurrences associated with the particular transducer, orwith phenomena occurring within sample 14 in the immediate vicinity ofthat transducer. In practice, however, simultaneous operation of morethan one transducer can result in cross-transducer noise components onindividual transducer output lines. For example, in a non-ideal noisysystem, the electrical signal on output line 18 a may have componentsresulting from the movement of transducers 12 b, 12 c or 12 d. Becausethese signal components typically are undesired and correspond totransducers other than transducer 12 a, they may be referred to ascross-transducer noise, or cross-transducer noise components.

[0022] In many embodiments, the transducers (e.g., transducers 12 a, 12b, 12 c and 12 d) are suspended relative to a base or other stationarystructure (not shown) with a mechanical suspension (not shown).Typically, the mechanical suspension is connected to all of thetransducers but is designed to allow each transducer to moveindependently. Moreover, the suspension structure is selected andspecifically designed to maximize this independence and thereby minimizecrosstalk, or cross-transducer coupling. Although the transducers aresubstantially independent of one another, there often is some undesiredcross-transducer coupling of vibrations and/or other movements throughthe suspension structure. Vibration of transducer 12 a, for example, maycouple through the mechanical suspension to produce a vibration intransducer 12 b. This would contribute a cross-transducer noisecomponent to the electrical signal on output line 18 b.

[0023] Typically, the various circuitry coupled with the transducers isat least partially isolated to facilitate obtaining noise-free outputsignals for each individual transducer. In practice, however, there isoften undesired electrical coupling between the circuitry ofsimultaneously active transducers. This may occur, for example, as aresult of stray capacitance, stray mutual inductance, and/or otherindirect electrical coupling. Stray capacitance between output lines 18a and 18 b, for example, could introduce undesired noise components intothe signals on those lines.

[0024] In many cases, it will be desirable to employ a liquid within oraround sample 14. In biological scanning systems, for example, liquidmay be employed to hydrate various types of sample materials. Typically,the liquid is provided within or around each portion of the samplematerial on one side of the transducer array, such that the transducerarray has a “wet side” and a “dry side,” as indicated in the example ofFIG. 1. Use of such a liquid environment can be another source ofcross-transducer noise, as discussed above.

[0025] As shown in FIG. 1, oscillator subsystem 16 may be configured toapply different variants of an oscillator signal to the other componentsof sensor system 10. Typically, the base signal is a sinusoid, and thesubsystem generates a number of phase-shifted variants of this signalfor use within sensor system 10. As explained in more detail below, thephase-shifted variants may be applied as inputs to produce vibrations orother movement in the transducers. In addition, as also explained below,the phase-shifted variants may be employed during processing of outputsignals produced by the transducers.

[0026] In the depicted embodiment, oscillator subsystem 16 is configuredto output four different variants of a sinusoidal local oscillator (LO)signal: (1) a first variant 30 a that is in phase with the LO, or 0°,(2) a second variant 30 b that is shifted in phase from the LO by 90°,(3) a third variant 30 c that is shifted in phase from the LO by 180°and (4) a fourth variant 30 d that is shifted in phase from the LO by2700. These phase-shifted variants typically are all the same frequencyas the local oscillator, and may be respectively referred to as the 0°variant, 90° variant, 180° variant and 270° variant.

[0027] As shown in FIG. 1, each of the different phase-shifted variantsmay be applied as an input to a corresponding one of the transducers. Inthe depicted example, the 0° variant is applied to transducer 12 a, the90° variant is applied to transducer 12 b, and so on. As explainedbelow, application of different phase-shifted variants to thetransducers may allow an output processing subsystem 34 to isolate andextract output signals from the individual transducers, free from thecross-transducer interference described above.

[0028] In order to suppress cross-transducer interference, it will bedesirable in many cases to employ the same phase-shifted variants duringprocessing of output signals produced by the transducers. Indeed,exemplary output processing subsystem 34 may be configured to employ thephase-shifted variants to isolate and extract output signals from thetransducers.

[0029] As in the depicted example, output processing subsystem 34 mayinclude, for each of transducers 12 a, 12 b, 12 c and 12 d, acorresponding mixer section (36 a, 36 b, 36 c and 36 d, respectively)and a low pass filter (38 a, 38 b, 38 c and 38 d, respectively) (LPF).Though depicted as separate devices, the individual mixer devices may becollectively referred to as a mixer, and the individual filter devicesmay be referred to as a filter. Indeed, the individual devices may beconsolidated into one or more single components configured to processmultiple signals. The filters may be implemented in a variety ofconfigurations, including configurations incorporating passive and/oractive filter components. Filtering may be achieved using a passive RCnetwork, for example. Additionally, or alternatively, active componentssuch as a digital signal processor may be employed to provide filtering.Filtering may be performed based on frequency and/or phase of incomingsignals. Indeed, in some embodiments, a digital signal processor isemployed to perform linear phase processing, so as to allow forrejection of unwanted signal components. To achieve the desired signalisolation, the digital signal processor may be configured to subtract,for a given transducer output, any out-of-phase, steady-statecomponents. In many cases, frequency filtering using linear-phasetopologies or algorithms facilitates channel separation and helps topreserve resultant pulse characteristics. Additionally, in order toachieve adjacent signal rejection in a system employing foursimultaneously active channels, it will often be desirable to limitphase deviation of the filter to ±45°.

[0030] An exemplary mode of operation for the depicted output processingsubsystem will now be described. Referring specifically to transducer 12a, the transducer may be stimulated by application of the 0° variant ofthe sinusoidal local oscillator signal. This, in turn, results inmovement of the transducer. As discussed above, the movement of thetransducer may depend on various factors other than the characteristicsof the input drive signal. Portions of sample 14 may, for example, bondto the surface of the transducer. The resulting variation in mass (i.e.,from an unloaded state) would cause a change in the resonant frequencyat which transducer 12 a vibrates. In addition, various “acoustic” or“sonic” events can affect the movement of transducer 12 a. For example,rupture events at or near the transducer surface (e.g., a portion ofsample 14 breaking away from a bonding location on the transducer, or abreaking of chemical bonds within sample 14) may produce a pressure wavethat acts upon the transducer.

[0031] The various different movements of transducer 12 a contribute tothe output signal arising on output line 18 a. As discussed above, inmost cases, it is preferable that the signal on output line 18 a reflectonly the physical characteristics of transducer 12 a and/or eventsoccurring within sample 14 in the immediate vicinity of transducer 12 a.However, if transducers other than transducer 12 a are simultaneouslyactive, the signal on line 18 a will typically include cross-transducernoise (i.e., noise resulting from the other active transducers).

[0032] For example, as discussed above, in many implementations,transducers 12 a and 12 b (as well as transducers 12 c and 12 d) areoperatively coupled to a stationary base with a shared mechanicalsuspension. Assuming a non-ideal mechanical suspension, vibrations oftransducer 12 a may cause transducer 12 b to vibrate, and/or vice versa,which in turn will contribute noise components to the electrical signalson lines 18 a and/or 18 b. Noise components can also arise from pressurewaves propagating through a liquid sample, and from indirect electricalcouplings in the transducer supporting circuitry, as also discussedabove.

[0033] In many prior systems, these noise issues are avoided byactivating only a single transducer at a time, or by ensuring thatsimultaneously active transducers are spaced apart so that noisecontributions are attenuated. This may, however, limit the processingcapacity of the sensor system. For example, constraints on theactivation of transducers typically will limit the speed of the sensorsystem. In biological scanning applications, for example, use of such asensor system may slow scanning operations and produce other processingbottlenecks.

[0034] When multiple transducers in the same area are simultaneouslyactive, the depicted use of different phase-shifted variants of the basedrive signal facilitates obtaining substantially noise-free outputsignals. Referring again to transducer 12 a and its supportingcircuitry, the signal on line 18 a is applied to mixer section 36 a,along with the same phase-shifted variant 30 a (the 0° variant) that wasapplied as an input drive signal to transducer 12 a. Use of the samevariant that is used to drive the transducer may be referred to as a“synchronous” deployment within output processing subsystem 34, sincethe variant typically is in sync with the transducer output signal online 18 a. The mixing at section 36 a creates sum frequencies anddifference frequencies, which are selectively filtered using LPF 38 a.LPF 38 a is tuned to pass only a range of frequencies and phasecorresponding to transducer 12 a. The resulting signal on output line 40a is therefore substantially free of cross-transducer noise.

[0035] As indicated above, some cross-transducer noise coupling mayoccur. However, the predetermined phase differences between thetransducer drive signals cause the noise from other transducers to haveelectrical characteristics that are distinct from the desired baseoutput signal. The characteristics of the noise signal(s) allow thenoise to be readily suppressed or removed via thefrequency/phase-dependent filtering that occurs at filters 38 a, 38 b,38 c and 38 d. For example, assume transducers 12 a and 12 b are bothactivated at the same time with their respective phase-shiftedoscillator variants (e.g., variants 30 a and 30 b). Movements oftransducer 12 a could produce a noise movement in transducer 12 b, viapressure wave coupling occurring through the liquid in sample 14, orthrough the transducer mechanical suspension. This would contributenoise to the electrical output signal on line 18 b. Additionally, oralternatively, a stray capacitance could couple noise onto the outputline. However, the phase differences between the oscillator signals usedwith each transducer would cause such noise contributions to appear online in a manner that would readily enable the noise to be filtered fromthe output signal.

[0036] More specifically, in certain multiple-transducer embodiments,employing different variants of a periodic signal may cause any“non-pure” (e.g., noisy) transducer output signal to have frequencycomponents that are distinct from those of the noise-free base output.Without noise, for example, the signal on a given output line typicallywould have a frequency close or identical to that of the base localoscillator signal. Because different transducers within a given groupwould be driven with different phase-shifted versions of the localoscillator, their vibratory outputs would be staggered in time relativeto one another. Accordingly, if vibration from more than one transducerwere to contribute to the output on any given transducer output line,the resulting noisy output would have higher frequency components thanthe noise-free output. The noise components would then be filtered outby the combined operation of the mixer sections andfrequency/phase-based filtering.

[0037] As indicated above, use of different drive signal variants may beimplemented in a number of different ways. The depicted illustrativeembodiment may, for example, be extended to more or less than four drivesignal variants that are equally distributed in phase over the period ofthe base oscillator signal. Assuming a modified system with Ntransducers, the modified system may be implemented with N correspondingdrive signal variants, one for each transducer. The drive signalvariants would be shifted in phase from the local oscillator by 0°,(1/N*360)°, (2/N*360)°, . . . and ((N−1)/N*360)°.

[0038] Furthermore, variations other than phase offsets may be employed,such as variations in frequency, amplitude, waveform type, etc. Indeed,the description should be understood to encompass use of any type ofdrive signal variations that facilitate isolating desired transduceroutputs from cross-transducer noise components. Typically, as in thespecific illustrative examples above, each transducer within a group isdriven by its own unique variant (e.g., a variant that can bedistinguished from those used to drive the other transducers within thegroup). This causes each transducer to have a characteristic response,such that when that response is undesirably coupled into the outputchannel of another transducer (e.g., as noise), the undesired componentson the channel can be readily identified and removed through varioustechniques, such as frequency/phase-based filtering, adaptive filtering,excitation signal subtraction and the like.

[0039] The drive signal circuitry that provides the signal variants tothe transducers may also be implemented in many different ways. As shownin FIG. 1, each transducer group 12 may be provided with an oscillatorsubsystem 16 dedicated to that individual transducer group.Additionally, or alternatively, a global oscillator generator 96 (FIG.2) may be provided to provide oscillator signals (and variants thereof)to the individual transducer groups 22, via multiplexing, switchingand/or other devices/methods.

[0040] A transducer-based sensor method will now be described withreference to FIG. 3. The method may be implemented in a variety ofdifferent ways. The following description is merely an illustrativeexample. As shown at 60 in FIG. 3, the exemplary implementation of themethod includes applying a first phase-shifted variant of a periodicsignal to a transducer. The implementation also includes applying asecond, different variant of the periodic signal to another transducer,as shown at 62. As with the embodiments described above, furthervariants may be employed as desired and appropriate for a givenapplication, as indicated at 64.

[0041] As explained above, the differences between the signal variantstypically will cause signals associated with the two transducers to havedifferent characteristics. This, in turn, will cause a noisy outputsignal (e.g., a signal having components associated with more than oneof the transducers) to have characteristics that differ from those ofthe noise-free signal. Typically, the differences between a noisy signaland a noise-free signal manifest as differences in frequency orfrequency ranges, such that noise suppression can be readily performedvia bandpass filtering. Indeed, the depicted exemplary implementationincludes, at 66, filtering output signals based on frequency to removecross-transducer noise. Also, as explained above, phase discriminationmethods may be employed in addition to or instead of frequency-basedfiltering.

[0042] It should be understood that the depicted implementation can beextended to more than two transducers and two corresponding drive signalvariants. For example, as in the exemplary systems described above, itwill often be desirable to employ four signal variants (e.g.,respectively shifted in phase from a base signal by 0°, 90°, 180° and270°) in a quadrature scheme with groups of four transducers. Indeed, itshould be appreciated that the described method may be implemented inconnection with the systems described above, and may thus be modified inaccordance with the various different configurations that may beemployed with those systems. It should be understood, however, that themethod is broadly applicable and need not be implemented in connectionwith the particular systems described above.

[0043] It should be understood that the above systems and methods may beapplied to a wide variety of multiple-transducer applications where itis desirable to obtain relatively noise-free outputs from individualtransducers. As explained in the specific exemplary implementationsdiscussed above, multiple variants of a drive signal are applied todifferent transducers in the system. Use of the different variations ofthe drive signal allow signal contributions from the differenttransducers to have different characteristics. This, in turn,facilitates suppression of noise components, through use of filtering orother techniques.

[0044]FIG. 4 depicts yet another embodiment of a transducer-based sensorsystem 100. Similar to the previously described embodiments, system 100may include a drive signal generator 102 that is coupled with atransducer 104. Transducer 104 may be placed near or into contact with asample 106. The drive signal generator produces a drive signal,typically an oscillating sinusoidal signal, which is applied as an inputto transducer 104.

[0045] Typically, application of the drive signal to the transducercauses the transducer to move. In the case of an oscillatory signal, theresulting movement normally is in the form of reciprocating vibration.Movement of the transducer affects an electrical output signal producedby the transducer. As in the previously described exemplaryapplications, analysis of the transducer output signal may yieldinformation about the transducer itself, material from sample 106 thathas bonded to the transducer, bonds breaking within sample 106, etc.

[0046] In many cases, it will be desirable that transducer 104 be drivenso as to maximize its mechanical excursions (e.g., so as to causereciprocal vibrations with as high a physical amplitude as possible).Typically, this will be achieved by driving the transducer with anoscillatory signal tuned to the resonant frequency of the transducer.With many existing silicon fabrication methods, transducer arrays willvary in resonant frequency from batch to batch. Even within a givenarray, there may be some variation in resonant frequency betweentransducer groups, or between individual transducers.

[0047] Accordingly, drive signal generator 102 may be configured with aprogrammable capability, in order to ensure that drive signals areprovided to yield the desired transducer response. In the depictedexample, drive signal generator 102 may be implemented as a directdigital synthesizer (DDS) to facilitate control over the drive signalsapplied to the transducers. Use of such a device, for example, allowsthe oscillatory drive signal to be provided at a frequency matched tothe resonant frequency of transducer 104, or to some other desiredfrequency.

[0048] The depicted embodiment includes only one transducer, though itwill be appreciated that system 100 may be provided with any practicablenumber of transducers, and transducers may be organized into groups asin the previously described embodiments. Where multiple transducers areemployed, the system depicted in FIG. 4 may also be adapted to employmultiple different drive signal variants, as described above withrespect to the previous embodiments. Use of a DDS in such a setting canfacilitate provision of different drive signal variants (e.g., multiplephase-shifted variants of a base sinusoidal drive signal). For example,use of a DDS readily enables introduction of desired predetermined phasedelays to produce drive signal variants.

[0049] As in the previously described embodiments, sensor system 100includes an output processing subsystem 110 configured to process outputfrom transducer 104 (or from multiple transducers). As indicated, outputprocessing subsystem 110 may include a device 112 adapted to receive andprocess output from transducer 104. In addition, device 112 typically iscoupled with signal generator 102, such that the same oscillatory signalthat drives the transducer is also applied directly to device 112.

[0050] In the depicted example, device 112 is implemented as a mixer. Itwill be appreciated that the mixed signals in the example are at leastsubstantially synchronous, or contain synchronous components, that is,components of the same frequency and/or phase. Operation of the mixerand accompanying components (to be described) facilitates detection ofsignals in sync with the base drive signal. Device 112 and itsaccompanying components may therefore be considered a synchronousdetector, or alternatively, a synchrodyne or homodyne.

[0051] In the depicted embodiment, mixing of the two signals produces anintermediate output from the mixer that contains components with sumfrequencies and difference frequencies. The intermediate output may alsovary considerably in the phase relationships of its signal components,relative to the base drive signal. In many implementations, the abilityto effectively remove unwanted components from the intermediate outputdepends on being able to predict how the processing system will performin the presence of signals with such widely varying characteristics.

[0052] In many cases, accurate, noise-free signal extraction will beimproved by increasing linearity of various aspects of output processingsubsystem 110. This may be accomplished by presenting device 112 with aconstant and/or matched output impedance for its expected range ofoutput signals. As indicated above, the provided impedance may beselected to correspond to the varying phase, frequency, and othercharacteristics of the signal components in the intermediate outputgenerated by device 112. For example, the impedance may be selected toprovide linear phase response across desired frequencies, and/or may beselected so as to realize a consistent impedance response across desiredfrequencies, to thereby maintain signal integrity for the intermediatesignal components.

[0053] Accordingly, as in the example shown in FIG. 4, output processingsubsystem 110 may be provided with an impedance-matching device, such asdiplexer 116, which typically is coupled to device 112 (e.g., the mixer)so as to receive the intermediate mixed output. Diplexer 116 may beconfigured to present a matched and/or constant output impedance todevice 112 for the expected operational range of signal components.Without such a matched and/or constant impedance, the termination of thesignal channel will be at least partially incomplete, and signalreflections and other effects may occur. These effects can complicateextraction of noiseless output for a given transducer. In sensorapplications (e.g., rupture event scanning and quartz crystalmicrobalance applications), these effects can have an adverse impact onthe accuracy of the sensor.

[0054] Use of diplexer 116, or a like device, to provide a matched orconstant impedance, may be particularly advantageous in a setting wheremultiple drive signal variants are employed. In the embodiments andmethod implementations described above, individual transducers within agroup may be driven by oscillator variants that are in different phaserelationships to the base oscillator drive signal. One potential resultof using multiple phase-shifted variants is that the transducer outputscan exhibit a greater variation in characteristics (e.g., phase andfrequency) than would be expected if only a single oscillator signalwere used to drive the transducers. The increased variation in thecharacteristics of the intermediate output (e.g., the output from mixerdevice 112) may complicate design issues relating to the output signalchannel. In particular, the increased signal variation increases thepotential for a partially non-terminated signal channel, which may leadto the signal reflections and the other undesirable effects discussedabove. Provision of the matched and/or constant impedance (e.g., throughuse of a diplexer for each of the transducers) can stabilize theperformance of the output signal channel(s). This stabilizationtypically will enhance the ability to extract a desired noiselessoutput, through use of frequency-based filtering, phase discrimination,and the other methods described herein.

[0055] Filter 114 may be provided to further facilitate extraction ofthe desired output signal for transducer 104, or for a given transducerin a multiple-transducer configuration. As in the previously describedembodiments, filtering may be performed with a digital signal processor,with active or passive components, and may be performed based on phaseand/or frequency to achieve the desired signal isolation.

[0056] In some transducer applications, the signal channel may beconfigured such that both input drive and output response signalscoexist on the same channel or signal path. In many cases, this cancomplicate processing of output signals. For example, in such a setting,it may be difficult to discern whether certain signal characteristicsare produced directly by the transducer drive signal, or from movementof the transducer(s). It should be appreciated that the drive signalcharacteristics normally are known, and therefore are not of interest inmost applications. The goal in most sensor applications is not to studythe drive signal, but rather to obtain information about the transducerand its immediate environment (e.g., the mass of the transducer, thequantity of sample material that has bonded to the transducer, etc.).

[0057] This issue may be addressed with a cyclically repeated “drive andlisten” method. In such a method, the transducer(s) is driven viatemporary application of the drive signal. Shortly after the drivesignal is deactivated, the system response is sampled, for example byreading the output for a given transducer into a storage location, suchas FIFO buffer 120. This process is performed repeatedly, to obtain asample of data over time, and then various time domain and/or frequencydomain analyses may be performed on the accumulated data. Depending onthe application, the analytical methods that may be applied includeFourier transformations and Hartley/Bracewell transformations, amongother methods. In rupture event scanning, for example, these methods maybe applied to analyze acoustic emissions produced by rupture or otherevents.

[0058]FIG. 6 schematically depicts an exemplary circuit 200 that may beused to alternately drive and sample transducer signals. As indicated,circuit 200 typically will include some of the components discussed withreference to the other figures. Referring specifically to the figure,circuit 200 may include a direct digital synthesizer 202 that can be fedwith a digital signal processor (DSP) to facilitate generator oftransducer drive signals. The generated signal may be processed with adivider 204 and mixed with oscillator 206. The drive signal path mayalso include a signal gate 208, transducer drive amplifier 210 andcoupler 212. Accordingly, drive signals generated by the DSP andoscillator 206 may be applied as inputs to transducer 214. The outputsignal path may include signal gate 216, amplifier 218, sampler 220,analog-to-digital converter 222 and buffer 224. The resultant sampledoutput signal can then be applied to the DSP for time domain and/orfrequency domain analysis. As indicated, the input signal may be mixedinto the output signal path (e.g., via mixer 226), to provide thesynchronous detection capability previously discussed. Typically, acontroller 228 is also provided to control the timing of the drive andsample cycles.

[0059] It will be appreciated that when input drive and output responsesignals coexist on the same channel or signal path within one of thedescribed systems, that the input and output signals often move inopposite directions. In such a case, it may be advantageous to have a“duplexing” feature, that is, the ability to separate a transmitted ordrive signal from the received or resultant signal. Accordingly, ahybrid RF device, such as four-port hybrid RF device 118, may beemployed to facilitate segregation of the two signals. The directionalnature of the device eliminates the need for the alternating drive andlisten method referenced above. Drive signals may be applied to thetransducers while simultaneously sampling transducer output. The hybridRF device may be coupled to the other components in various topologies,though it will often be advantageous to couple the hybrid device to thediplexer output, as in the depicted example.

[0060]FIG. 7 depicts an exemplary topology showing how a hybrid RFdevice may be employed with the systems and methods described herein. Asshown, a transducer drive signal (TX) may be applied to 4-port hybrid RFdevice 240 via transducer drive amplifier 242, in order to drivetransducer 244. A resistive load 246 may be coupled to a third port ofdevice 240. The fourth port of device 240 couples into the output signalpath. As shown, the output signal path may include a common-mode rejectdevice 248, to facilitate rejection of the input drive signal.Accordingly, the depicted 4-port RF topology allows for simultaneousdriving and sampling of transducer 244, while eliminating or at leastreducing interference caused by co-existence of input and output signalson the signal channel associated with transducer 244.

[0061] It should be further emphasized that the devices and methodsdescribed with reference to FIG. 4 may all be advantageously employed inthe context of a multiple-transducer system with drive signal variants,such as that described above. Use of matched impedances, for example viadiplexer 116, can greatly simplify extraction of noise free transduceroutputs in a system employing multiple drive signal variants.

[0062]FIG. 5 depicts another implementation of a sensor method employingone or more transducers. The depicted method may be advantageouslyemployed with the embodiments described above, or in connection withother systems. The method includes, at 130, applying a drive signal to atransducer array. The transducer array may include one or moretransducers of any suitable type. As described above, multipletransducers may be employed along with drive signals having varyingphase/frequency relationships with a base drive signal.

[0063] At 132, the method includes mixing output from the transducerarray with the transducer drive signal. This may include, inmultiple-transducer embodiments, mixing the output from a giventransducer with a copy of the same drive signal variant that was used todrive the transducer. Such an implementation is described with referenceto the embodiment of FIG. 1, and particularly in connection with thesignals applied as inputs to mixer sections 36 a, 36 b, 36 c and 36 d.

[0064] The mixed output may then be provide along an output signal pathhaving a matched impedance, as shown at 134. In particular, the outputsignal path may be provided with a diplexer, as discussed above, toprovide a matched and/or constant output impedance in the output signalpath of the mixing device, for the expected range of signalcharacteristics. As shown at 136, the method may also include channelingsignal flow (e.g., the output from the impedance-calibrated device)through a hybrid RF device. More specifically, in typicalimplementations of the method, signal flow is provided through afour-port hybrid RF device. The directional characteristics of thehybrid device allow transducer outputs to be sample while simultaneouslyapplying drive signals to the transducers.

[0065] As shown at 138 and 140, the method may also include removingunwanted signal components (e.g., to obtain a substantially noise-freeoutput for a given transducer) and performing various types of analysison the final output. For example, Fourier or Hartley/Bracewelltransformations may be applied to the output date to analyze acousticemissions detected by the transducers. In addition, wherefrequency-based filtering is employed to remove unwanted signalcomponents, it will often be desirable to employ linear phase filtertopologies and/or filtering techniques, as discussed above.

[0066] While the present embodiments and method implementations havebeen particularly shown and described, those skilled in the art willunderstand that many variations may be made therein without departingfrom the spirit and scope defined in the following claims. Thedescription should be understood to include all novel and non-obviouscombinations of elements described herein, and claims may be presentedin this or a later application to any novel and non-obvious combinationof these elements. Where the claims recite “a” or “a first” element orthe equivalent thereof, such claims should be understood to includeincorporation of one or more such elements, neither requiring norexcluding two or more such elements.

What is claimed is:
 1. A transducer-based sensor system, comprising: adrive signal generator for generating a drive signal; a transducercoupled to the drive signal generator and configured to receive thedrive signal; a mixer coupled to the transducer and configured toreceive output from the transducer and mix such output with the drivesignal generated by the drive signal generator, where such outputresults at least in part from physical movement of the transducer; and adiplexer operatively coupled with the mixer and configured to present asubstantially matched output impedance to the mixer over an operativerange of output frequencies.
 2. The sensor system of claim 1, furthercomprising a hybrid RF device coupled to the diplexer within an outputsignal path associated with the transducer, the hybrid RF device beingconfigured to segregate signals flowing in different directions alongthe output signal path.
 3. The sensor system of claim 2, where thehybrid RF device is configured to enable sampling of output from thetransducer simultaneously while the transducer is being driven by thedrive signal, the hybrid RF device being configured to reduce, duringsuch sampling of output from the transducer, interference contributed bythe drive signal to the output signal path.
 4. The sensor system ofclaim 1, further comprising a filter coupled downstream of the mixer andconfigured to extract noise from an intermediate transducer outputsignal so as to produce a final transducer output signal, where thefilter is configured to perform such filtration based on at least one offrequency and phase.
 5. The sensor system of claim 1, further comprisinga plurality of transducer groups, each having a plurality of transducersconfigured to be placed into operative proximity with a sample material.6. The sensor system of claim 5, where the transducer-based sensorsystem is configured so that, within each transducer group, eachtransducer is driven by a different phase-shifted variant of the drivesignal.
 7. The sensor system of claim 6, where each transducer groupincludes four transducers, and where the transducers within a givengroup are configured to be driven by drive signal variants that arerespectively shifted in phase from the drive signal by 0°, 90°, 180° and270°.
 8. The sensor system of claim 6, where each transducer groupincludes N transducers that are driven by N corresponding phase-shiftedvariants that are respectively shifted in phase from the localoscillator signal by 0°, (1/N*360)°, (2/N*360)° . . . and((N−1)/N*360)°.
 9. A transducer-based sensor system, comprising: atransducer configured to produce electrical output based on movement ofthe transducer; an output processing subsystem operatively coupled withthe transducer, the output processing subsystem including: a mixerconfigured to mix electrical output of the transducer with anoscillatory signal that is synchronous with an expected component of thetransducer's electrical output, the oscillatory signal being therebyconfigured to facilitate synchronous detection of the expectedcomponent; an impedance coupled within an output signal path associatedwith the transducer, the impedance being configured to present asubstantially matched output impedance to the mixer over an operativerange of frequencies, the impedance being further configured to minimizesignal reflections so as to simplify downstream rejection of unwantedsignal components.
 10. The sensor system of claim 9, further comprisinga hybrid RF device coupled within the output signal path, the hybrid RFdevice being configured to segregate signals flowing in differentdirections along the output signal path.
 11. The sensor system of claim10, where the hybrid RF device is configured to enable sampling ofoutput from the transducer simultaneously while the transducer is beingdriven, the hybrid RF device being configured to reduce, during suchsampling of output from the transducer, interference contributed by anactivation signal applied as an input to drive the transducer.
 12. Thesensor system of claim 9, further comprising a drive signal generatorconfigured to apply a drive signal as an input to the transducer todrive the transducer.
 13. The sensor system of claim 12, where the drivesignal and the oscillatory signal are substantially in phase and ofsubstantially the same frequency.
 14. The sensor system of claim 12,where the drive signal and the oscillatory signal are of substantiallythe same frequency, but offset in phase by a predetermined amount. 15.The sensor system of claim 12, where the drive signal generator isprogrammable, to enable matching of the drive signal to a resonantfrequency of the transducer.
 16. The sensor system of claim 9, furthercomprising a plurality of transducer groups, each having a plurality oftransducers configured to be placed into operative proximity with asample material.
 17. The sensor system of claim 16, where within eachtransducer group, each transducer is configured to be driven by adifferent phase-shifted variant of a local oscillator signal.
 18. Thesensor system of claim 17, where each transducer group includes a firsttransducer configured to be driven by a variant shifted in phase by 0°from the local oscillator signal, a second transducer configured to bedriven by a variant shifted in phase by 90° from the local oscillatorsignal, a third transducer configured to be driven by a variant shiftedin phase by 180° from the local oscillator signal and a fourthtransducer configured to be driven by a variant shifted in phase by 270°from the local oscillator signal.
 19. The sensor system of claim 17,further comprising a programmable drive signal generator configured toprovide the local oscillator signal and enable tuning of a frequency ofthe local oscillator signal to correspond to a desired resonantfrequency associated with the transducer-based sensor system.
 20. Atransducer-based sensor system, comprising: a transducer configured toproduce electrical output based on movement of the transducer; asynchronous detector operatively coupled to the transducer andconfigured to produce, in response to application of electrical outputfrom the transducer, plural signal components in an operative range offrequencies, where such plural signal components are subject tosubsequent downstream processing to extract a desired, substantiallynoise-free output signal associated with the transducer; and a matchingdevice coupled with the synchronous detector and configured to presentthe synchronous detector with a substantially matched output impedanceover the operative range of frequencies, to enhance linearity inprocessing of electrical output from the transducer.
 21. The sensorsystem of claim 20, where the matching device includes a diplexer. 22.The sensor system of claim 20, further comprising a drive signalgenerator configured to apply a drive signal to the transducer.
 23. Thesensor system of claim 22, where the drive signal generator isoperatively coupled with the synchronous detector, the synchronousdetector being configured to mix the drive signal with electrical outputfrom the transducer.
 24. The sensor system of claim 20, furthercomprising a hybrid RF device positioned within an output signal pathassociated with the transducer.
 25. The sensor system of claim 20,further comprising a plurality of transducer groups, each transducergroup including a plurality of transducers, where within each transducergroup, each transducer is configured to be drive by a differentphase-shifted variant of an oscillatory drive signal.
 26. The sensorsystem of claim 25, where each transducer group includes a firsttransducer configured to be driven by a variant shifted in phase by 0°from the local oscillator signal, a second transducer configured to bedriven by a variant shifted in phase by 90° from the local oscillatorsignal, a third transducer configured to be driven by a variant shiftedin phase by 180° from the local oscillator signal and a fourthtransducer configured to be driven by a variant shifted in phase by 270°from the local oscillator signal.
 27. The sensor system of claim 25,where each transducer has an associated output signal path, each outputsignal path including: a synchronous detector operatively coupled to thetransducer and configured to produce, in response to application ofelectrical output from the transducer, plural signal components in anoperative range of frequencies, where such plural signal components aresubject to subsequent downstream processing to extract a desired,substantially noise-free output signal associated with the transducer;and a matching device coupled with the synchronous detector andconfigured to present the synchronous detector with a substantiallymatched output impedance over the operative range of frequencies, topromote linearity in processing of electrical output from thetransducer.
 28. A transducer-based sensor system, comprising: aplurality of transducers configured to be placed into operativeproximity to a sample material; a drive signal generator configured toapply electrical drive signals to the transducers to cause thetransducers to move; and an output processing subsystem configured toprocess electrical output produced by movement of the transducers, wherethe drive signal generator is programmable to adjustably provide anoscillatory drive signal having a frequency corresponding to a resonantfrequency of one of the transducers.
 29. The sensor system of claim 28,where the output processing subsystem includes: a mixer configured tomix electrical output of at least one of the transducers with anoscillatory signal that is synchronous with an expected component of thetransducer's electrical output, the oscillatory signal being therebyconfigured to facilitate synchronous detection of the expectedcomponent; an impedance coupled within an output signal path associatedwith the at least one of the transducers, the impedance being configuredto present a substantially matched output impedance to the mixer over anoperative range of frequencies, the impedance being further configuredto inhibit signal reflections so as to simplify downstream rejection ofunwanted signal components.
 30. The sensor system of claim 29, where theimpedance is implemented with a diplexer coupled within the outputsignal path.
 31. The sensor system of claim 29, further comprising ahybrid RF device coupled within the output signal path.
 32. The sensorsystem of claim 28, where the plurality of transducers are provided ingroups, each group containing a plurality of transducers, and wherewithin each group, each transducer is configured to be driven by adifferent phase-shifted variant of a local oscillator signal.
 33. Atransducer-based sensor method, comprising: producing an electricaloutput signal based at least in part on movements of a transducer;applying the electrical output signal to a synchronous detector;applying a local oscillator signal to the synchronous detector, therebycausing the synchronous detector to output plural output signalcomponents in an operative range of frequencies; and outputting theplural output signal components along an output signal path having animpedance, where the impedance is configured to present a substantiallymatched output impedance to the synchronous detector over the operativerange of frequencies.
 34. A transducer-based sensor method, comprising:driving a transducer array to cause transducer movement and acorresponding electrical output signal; applying the electrical outputsignal to a synchronous detector; applying an oscillatory signal to thesynchronous detector, thereby causing the synchronous detector to outputplural output signal components in an operative range of frequencies;and providing the plural output signal components along an output signalpath having an impedance, where the impedance is configured to provide asubstantially matched output impedance to the synchronous detector forthe operative range of frequencies.
 35. The sensor method of claim 34,where driving the transducer array includes applying a drive signal toeach of a plurality of transducers of the transducer array.
 36. Thesensor method of claim 35, where driving the transducer array includesapplying different phase-shifted variants of a local oscillator signalto transducers within the array.
 37. The sensor method of claim 34,where the plural output signal components include unwanted components,the method further comprising performing frequency-based filteringwithin the output signal path to remove the unwanted components.
 38. Atransducer-based sensor system, comprising: drive signal generator meansfor generating a drive signal; transducer means for receiving the drivesignal, the transducer means being operatively coupled to the drivesignal generator means; mixer means for receiving output from thetransducer means and mixing such output with the drive signal generatedby the drive signal generator means, where such output results at leastin part from movement of the transducer means; and diplexer means forpresenting a substantially matched output impedance to the mixer meansover an operative range of output frequencies, the diplexer means beingoperatively coupled to the mixer means.